Attenuated total reflectance (ATR) is an optical interrogation technique often used in conjunction with infrared spectroscopy (e.g., Fourier Transform Infrared (FTIR)), which enables samples to be examined directly in a solid or liquid state.
In particular, ATR capitalizes on total internal reflected light produced at the interface of a configured internally reflecting element (IRE) and a coupled sample plane. In operation, a beam of light (e.g., infrared) is passed through the IRE crystal in such a way that it reflects at least once off of the internal surface in contact with the sample. This reflection forms an evanescent wave which extends into the sample, often up to about 5 microns, with the exact value being determined by the wavelength of light, the angle of incidence and the indices of refraction for the IRE crystal and the sample medium being interrogated. The reflected beam, which carries the spectral information of the sample, is thereafter interrogated for analysis via, for example, a single pixel, linear array or 2 dimensional array detector.
Raman spectroscopy is an optical interrogation, which enables samples to be examined directly in solid, liquid or gas state.
Raman, has the advantage, in backscatter collection mode that it can collect data through transparent containers, such as vials, bottles and plastic bags. In operation, a beam of monochromatic laser light is directed at and into the sample. This induces the molecules in the sample to vibrate, consuming some of the laser energy. Light is rescattered from the sample, and the rescattered light contains spectral information that is unique to the sample. This is thereafter interrogated for analysis, via, for example a charge-coupled-detector (CCD), linear or 2-dimensional array detectors or a InGaAs linear array or 2 dimensional array detector.
The workflow of handheld FTIR and/or Raman spectrometers requires an operator to perform specific steps in order to have the instrument perform correctly. One of the most common issues with the FTIR workflow using ATR/FTIR hand-held spectrometers is that a first responder donned in, for example, a hazmat suit, has difficulty in following the workflow to successfully execute a scan of a desired sample, primarily because of limited visibility and dexterity. The issue of visibility is exacerbated by the fact that the user is not able to read instructions on the screen, because the mask of the suit often can be fogged as a result of the user operating in the field.
Accordingly, a need exists for a means to allow a first responder operator of hand-held spectrometers to obtain scans of samples in hazardous conditions without having to read specific operating instructions. The present invention is directed to this need by providing a compact hand-held spectrometer that is configured to provide visual indicators close to the sensing area so that the user can operate the device without reading the screen.